Spittlebug foam is unsightly but harmless. Control these insects by removing them individually or by washing them off with a strong spray of water.
Photo/Illustration: Allison Starcher
Charles W. G. Smith, a horticulturist in Mill River, Massachusetts, answers: The white froth on your plants is called spittle and is produced by spittlebugs (nymphs of the adult froghopper insect). The foam itself is unsightly but harmless. The spittlebug that hides inside the foam is a different matter and can, depending on the species of the insect, be everything from an unattractive nuisance to a significant pest.
Spittlebugs look like leafhoppers and, like aphids and adelgids, use their piercing mouthparts to feed on plants by sucking out the sap. Each dollop of foam, a mix of slimy sugary insect excretions and air bubbles, encloses a single spittlebug and protects it from desiccation and predators like lacewings and ladybugs. Most species are bright green, with big bulging eyes, though they can also be white, yellow, brown, or even pale orange.
Many species of spittlebug are common in North America. Each spittlebug species is most often host-specific, attacking a distinct plant or group of plants, such as holly, pine, strawberry, alfalfa, or juniper, as well as many herbaceous perennials and herbs. Spittlebug infestations are normally small and the damage to mature plants is usually limited to yellow spots on the leaves. The foamy spittle usually appears from May to October in warm humid regions and for a few weeks around the summer solstice in more temperate climates.
You can control spittlebugs by handpicking them from the foam or by washing them off the plants with a strong spray of water. Adult spittlebugs (froghoppers) lay their eggs in weedy places and in plant stubble where the eggs remain through winter. Extended control is often accomplished by keeping the area free of weeds and turning the soil to disturb egg-laying sites. Planting flowers such as alyssum (Alyssum spp. and cvs., Zones 4–9) to attract beneficial predatory insects like pirate bugs also helps.
Although spittlebugs are not often a severe problem, one species, the two-lined spittlebug, has become a serious pest of lawns in the South. Recognizable by the two orange stripes across their wings, two-lined spittlebugs feed on warm-season grasses that tend to produce thick thatch like Bermuda, St. Augustine, and zoysia. Their eggs overwinter in the grass stems and hatch in late spring. Then, for about four weeks, the nymphs feed on the grass plants down near the soil and thatch where the humidity is highest. Damage generally appears in stages, with the first being a widespread wilting of the grass blades in infested areas, followed by the appearance of yellow patches that turn brown as the grass dies.
To manage two-lined spittlebugs, mow the infested area and give it a deep watering in the morning on a warm dry day. Apply insecticidal soap thoroughly in the late afternoon of the same day, following the directions on the label. For extended control, reduce humidity in the lawn by removing thatch annually and strengthen the turf with a lawn fertilizer each spring.